Kadokado's Flushee game is difficult to master, but is pretty fun to play. It is in the kadokado puzzle games section and involves big lines of monsters that have to be grouped into sets of four or more to be eliminated. As monsters are eliminated the line drops and new monsters drop in from the top of the screen. Flushee is a free game on kadokado so you don't have to earn any points to buy it.
Part of the frustration with Flushee is that you can't control getting the powerups, and you only have 10 shots. The powerups in Flushee are super important. The apple is worth 1000 points and the spiral is worth 5000 points, which means that if you are lucky enough to get a spiral your score is going to be super high. In order to maximize your chances of benefitting from the apples, you should try to eliminate columns of monsters on the edges, that when when the apple falls it will be on an edge where you can easily knock it off the side and get your points.
Creating large chains is also very beneficial but it is difficult to set up because you don't know what is going to drop in from the top.